Fifteen prisoners from the U.S. military prison in Guantanamo Bay, Cuba, have been released to the United Arab Emirates in the largest transfer of detainees during the Obama administration.

The release of 12 Yemeni nationals and three Afghans comes amid a renewed push to whittle down the number of detainees at Guantanamo.

The Pentagon says 61 detainees remain at Guantanamo.

President Barack Obama is facing a looming deadline to close the prison before he leaves office as he promised to do when he was first elected.

But he faces opposition from many Republican lawmakers as well as some fellow Democrats.

"I think we are at an extremely dangerous point where there is a significant possibility this is going to remain open as a permanent offshore prison to hold people, practically until they die," said Naureen Shah, Amnesty International's U.S. director for security and human rights.

Shah added that keeping Guantanamo open gave cover to foreign governments to ignore international human rights.

"It weakens the U.S. government's hand in arguing against torture and indefinite detention," she said.

One of the detainees who was transferred is an Afghan national, identified as Obaidullah, who has spent more than 13 years at Guantanamo. He had been accused of hiding and storing mines to be used against American forces in Afghanistan.

"The continued operation of the detention facility weakens our national security by draining resources, damaging our relationships with key allies and partners, and emboldening violent extremists," Lee Wolosky, the State Department's special envoy for closing the Guantanamo detention center, said.

VOA Pentagon correspondent Carla Babb contributed to this report. Some information from Reuters was also used